A single personality trait is the foundation for almost all mental illness
A range of various mental illnesses, such as depression, substance abuse, and psychosis, are linked to the same personality trait, research suggests.
Neuroticism is one of the five higher-order personality traits and pretty much everyone has it to some extent.
People who score high on neuroticism are easily worried and are more likely to experience negative feelings such as fear, anger, frustration, jealousy, guilt, and loneliness. They tend to interpret common situations as threatening, or to feel that small challenges are hopelessly difficult.
Now Eivind Ystrøm, a professor at the Department of Psychology at the University of Oslo and his colleagues say that this trait best defines the risk of developing psychiatric problems.
Research also shows that it is mainly your genes that determine your personality, and thus the risk of mental illness.
And for better or worse, your upbringing probably has minimal effect.
All mental disorders are linked
"Previously we thought that mental illnesses such as depression, schizophrenia, bipolar disorder, and substance abuse, were completely separate diseases," Ystrøm says.
But research has now shown that these illnesses are often linked. If you suffer from one mental illness, you are more likely to develop another. And if someone in your immediate family has a psychiatric illness, your risk increases not only for this disorder, but for all other disorders.
These findings have led researchers to suspect that there could be a common underlying factor that increases an idividual's risk of mental illness, overall.
"At the same time there are also indications that personality and mental illnesses go hand-in-hand,” Ystrøm said. “People with mental illnesses systematically have a different personality than healthy people.”
What Ystrøm and colleagues have done is try to connect these factors. They asked: Can a specific personality trait constitute the one factor that underlies all mental disorders?
Twins shed light on inherited traits and environment
To find out, researchers used extensive data from the Twin Register at the Norwegian Institute of Public Health. Twin research can provide unique insights into how traits, genes, and environment, affect our lives.
Identical twins have similar genes. Sometimes twins are separated and grow up in different environments. If they grow up to be quite similar even though they have been raised by different families, this suggests that genes play a major role in determining their personalities. If they are not at all similar, it suggests that the environment is more decisive.
Fraternal twins, on the other hand, have different genes. If they grow up in the same home and develop similarly, this suggests that the environment is of great importance.
Ystrøm and colleagues have used new statistical methods to look for patterns in personality, mental disorders, genes, and environmental factors, among the twins in the Twin Register.
And the answer to the question the researchers asked is: yes, neuroticism seems to be the personality trait that best describes the risk of all mental disorders.
Genes probably determine the most
“This one trait doesn’t explain everything. Anyone can develop a mental illness. But these diseases are so closely linked to neuroticism that if you have a stable life and a lot of positive emotions associated with social contact, your chances of mental illness are significantly lower,” says Ystrøm.
Their study also shows that this trait is 50 per cent inherited.
“This means that mental disorders are generally associated with families. If one of your parents or siblings has a mental disorder, you are at a greater risk of all forms of mental illness,” he says.
And this is independent of the environment you grow up in.
"It's possible the environment is more important in determining the type of mental illness you develop,” Ystrøm says.
Nevertheless, he says, little is known about the factors that determine whether you develop depression or psychosis — or another mental disorder.
Supported by recent research
Svenn Torgersen, Professor Emeritus at the University of Oslo in Norway, who was not involved in the study, said the findings were well supported by previous research.
"If this study had come a few years ago, it would be very sensational," he says.
But in recent years there has been a wealth of research indicating that one basic factor lies behind different diagnoses and that neuroticism is likely a key factor, although it is not the only one, he says.
“This trait relates to how we tackle all of life’s challenges. It determines whether we have faith that we can do everything that we try to do or that we’ll never manage to succeed,” he says. "It relates to whether we are pessimistic and skeptical of other people, or whether we think the world is our oyster.”
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Read the Norwegian version of this article at forskning.no
